JP3759279B2 - Bidirectional optical communication module - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a time-division bidirectional optical communication module used for optical communication using an optical fiber.
[0002]
[Prior art]
For example, as shown in FIG. 3, a conventional bidirectional optical communication module includes a light emitting element 21 such as a semiconductor laser that generates transmission signal light, a photodiode that receives reception signal light through a half mirror 23, and a photo diode. A light receiving element 22 made of a transistor, a condensing lens 24 for coupling transmission signal light to an optical transmission path 25 such as an optical fiber, an optical transmission path 25 for transmitting the collected light, and an optical transmission path 25 The condensing lens 26 condenses the received signal light reflected by the half mirror 23 on the light receiving element 22. With this configuration, the transmission signal light from the light emitting element 21 enters the optical transmission line 25 via the half mirror 23 and is sent to the other party. When receiving a signal sent from the other party, the received signal light from the optical transmission path 25 is reflected by the half mirror 23 and converted into an electric signal by the light receiving element 22, and can be received. Is done. In this case, transmission and reception are alternately switched by time division, and mutual interference does not occur.
[0003]
In this configuration, it is necessary to assemble the light emitting element and the light receiving element independently through the half mirror in accordance with the optical axis of the condenser lens, and it is very difficult to assemble with high accuracy. Therefore, as shown in FIG. 4, without using a half mirror, the light receiving surface of the light receiving element 22 is received as a half reflecting surface, and the light from the light emitting element 21 is reflected to reflect the condensing lens 24 or light (not shown). A configuration coupled to a transmission path is also disclosed in, for example, Japanese Patent Application Laid-Open No. 8-114726.
[0004]
[Problems to be solved by the invention]
In the optical communication module having the above-described configuration, light incident on the optical transmission path from the light emitting element is approximately 50% by the half mirror or the light receiving element, and is emitted so that the return light is reflected and does not enter the optical transmission path. It is necessary to incline the light emitting surface of the element with respect to the axis of the light beam (a loss of about 50%), which attenuates to about 25% (0.5 × 0.5) of the light emitted from the light emitting element. Also, the received signal light incident on the light receiving element from the optical transmission path is attenuated to about 50% by the reflecting surface formed on the light receiving surface of the half mirror or the light receiving element. In the configuration using the half mirror, the light receiving surface must be inclined with respect to the beam of the received signal light so that the reflected light from the light receiving element does not return to the optical transmission path as in the case of the light emitting element, and the total is 25%. Attenuates to a degree. For this reason, the coupling efficiency between the light emitting element or the light receiving element and the optical transmission path is lowered, and a light emitting element having a large output or a light receiving element with high sensitivity must be used, resulting in an increase in cost.
[0005]
The present invention has been made to solve such a problem, and improves the coupling efficiency between the light emitting element and the light receiving element and the optical transmission path, reduces the number of parts, simplifies assembly, and is inexpensive and has characteristics. An object is to provide a stable bidirectional optical communication module.
[0006]
[Means for Solving the Problems]
A bidirectional optical communication module according to the present invention includes a light emitting element that generates a transmission signal, a condensing lens that couples transmission signal light from the light emitting element to an optical transmission path, and a received signal light from the optical transmission path. A light receiving element for receiving, and the light emitting element is provided so that transmission signal light from the light emitting element is directly coupled to the optical transmission line via the condenser lens, and the received signal light from the optical transmission line is provided. The light receiving element is provided at a position where the reflected light from the light emitting surface of the light emitting element can be received.
[0007]
With this configuration, although there is attenuation by tilting the light emitting element and the light receiving element with respect to the beam, light emitted from the light emitting element does not pass through an attenuation component of about 50%. In addition, the received signal light from the optical transmission path receives light reflected by the light emitting surface of the light emitting element, and thus partially attenuates, but the reflectance of the light emitting surface can be made higher than 50%. Both the light receiving element and the light receiving element can increase the coupling efficiency with the optical transmission line.
[0008]
Specifically, the light-emitting element is provided on the optical axis of the condenser lens so that the light-emitting surface is inclined with respect to the optical axis, and the light-receiving element has the light-receiving surface described above. The reception signal light from the optical transmission line is formed so as to be inclined with respect to the reflected beam by the light emitting element.
[0009]
A multilayer insulating film is formed on the light emitting surface of the light emitting element, and the reflectance on the light emitting surface is adjusted to 30 to 90% by the multilayer insulating film, thereby increasing the coupling efficiency of both the light emitting element and the light receiving element. be able to. Note that when the reflectance of the light emitting surface is increased, the light emission rate of the light emitted from the light emitting element is reduced, but the oscillation in the laser resonator of the light emitting element becomes stronger and the oscillation start current (I _th ) can be lowered. .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, the bidirectional optical communication module of the present invention will be described with reference to the drawings.
[0011]
The optical communication module of the present invention has a light emitting element 1 for generating a transmission signal and a transmission signal light from the light emitting element 1 to an optical transmission line 5 as shown in FIG. A position where the condensing lens 4 to be coupled and the light receiving element 2 for receiving the received signal light from the optical transmission path 5 can receive light reflected by the light emitting element 1 of the received signal light from the optical transmission path 5 The light receiving element 2 is provided. In the example shown in FIG. 1, the mount base 6 is fixed to the stem 7 to which the lead 8 is fixed, and the light emitting element 1 and the light receiving element 2 are fixed to the mount base 6. The structure is obtained by simply fixing both elements to 6.
[0012]
The light emitting element 1 is formed, for example, by fixing a semiconductor laser chip 1a that emits a laser beam B from a light emitting surface A that is an end face thereof to a submount 1b made of a silicon substrate or the like. The semiconductor laser has a light-emitting surface whose end face is made into a mirror surface by cleaving or the like, and a multilayer film made of an inorganic material such as amorphous Si or Al ₂ O ₃ is formed to appropriately set the reflectance with respect to the oscillation wavelength. In this structure, a resonator is formed by the light emitting layer and the multilayer film on the end face so that the resonator can oscillate. Therefore, the reflectance can be adjusted by adjusting the multilayer film, the oscillation intensity in the resonator can be adjusted, and the reflectance of the received signal light can also be adjusted by the multilayer film. In a light emitting device used as a normal optical communication module, the multilayer film is adjusted so that the reflectance at this end face is about 30%. However, even if this reflectance is about 30 to 90%, the resonator Although the ratio of the light emitted from the light source becomes small, it oscillates sufficiently and its intensity increases, so that the total light intensity does not decrease and the amount of light received by the light receiving element can be increased. This reflectance is preferably adjusted to about 50 to 90%, more preferably about 60 to 90%.
[0013]
By fixing the submount 1b of the light emitting element 1 to the mount base 6 with a low melting point metal such as In, the light emitting surface A is inclined with a predetermined angle with respect to the optical axis of the condenser lens 4 and positioned on the optical axis. It is attached as follows. The reason why the light emitting surface A is attached to be inclined with respect to the optical axis is that the received signal light from the optical transmission path 5 is reflected by the light emitting surface A and does not return to the optical transmission path 5 again, and the reflected light Is to be received by the light receiving element 2. Therefore, it is only necessary to tilt the reflected light so that it does not enter the condenser lens. As shown in an enlarged explanatory view of the light emitting element 1 and the light receiving element 2 in FIG. 2, it is perpendicular to the light emitting surface A of the light emitting element 1. The angle α between the bottom surface and the vertical direction that is the direction of the optical axis is tilted so as to be about 11.5 °, for example.
[0014]
The light receiving element 2 is composed of, for example, a photodiode, a phototransistor, a photocell, etc., and is attached so that the light receiving surface can receive the received signal light from the optical transmission path 5 reflected by the light emitting surface A of the light emitting element 1. It has been. The light receiving element 2 is disposed so that the light receiving surface is inclined without being perpendicular to the reflected beam from the light emitting surface A. The reason is to prevent the light reflected by the light receiving surface of the light receiving element 2 from returning to the light emitting surface and further returning to the optical transmission path 5. Therefore, it is sufficient that the reflected light from the light receiving surface does not return to the light emitting surface. In the example shown in FIG. 2, the angle β formed by the bottom surface parallel to the light receiving surface of the light receiving element 2 and the vertical direction is, for example, about 30 °. Tilted like that.
[0015]
The mount base 6 is made of, for example, iron, copper alloy, or the like, and is formed in advance so that the mounting surface of the light emitting element 1 and the mounting surface of the light receiving element 2 have the above-described angles. The device 2 can be easily assembled in the above-described relationship by simply bonding the element 2 to the mounting surface. A light (1) and a light receiving element (2) assembled to be aligned with the optical axis of the condenser lens (4) by covering the stem with a cap (not shown) to which the condenser lens (4) is attached. A communication module is obtained.
[0016]
Next, the operation of the optical communication module of the present invention will be described. First, when sending a signal, a light beam modulated by the signal is emitted from the light emitting element 1 and enters the optical transmission line 5 via the condenser lens 4. At this time, since the light emitting surface A of the light emitting element 1 is inclined with respect to the optical axis of the condenser lens 4, about 50% of the light emitted from the light emitting element 1 is combined with the condenser lens 4. . However, since there are no other parts to attenuate, it is sent to the other party through the optical transmission line with an intensity of about 50% of the emitted light. On the other hand, the received signal sent from the other party is reflected by the light emitting surface of the light emitting element 1 from the optical transmission path 5 through the condenser lens 4 and reaches the light receiving surface of the light receiving element 2 to be received. Since it is reflected by the light emitting surface A, the amount of light reaching the light receiving element differs depending on the reflectance. If the reflectance is 80%, for example, the reflected light spreads in addition to the light receiving element 2 and further 50%. Since it attenuates to the extent, it is received with an intensity of about 40% of the received light transmitted.
[0017]
That is, while the transmission side and the reception side are both attenuated to about 25% in the past, according to the present invention, the transmission side improves the coupling efficiency by a factor of about 50%, and the reception side also increases. Although it depends on the reflectance of the light emitting surface, if the reflectance of the light emitting surface is about 60 to 90%, the coupling efficiency is about 30 to 45% (40% when the reflectance is 80%, which is 60% improvement from the conventional one). ) In particular, since the attenuation on the transmitting side is small, the output can be reduced and the reflectance on the light emitting surface can be increased. By increasing the reflectance on the light emitting surface, the threshold current I _th (and hence the operating current I _op ) of the current to be oscillated can be lowered, and oscillation can be performed with a low input. If the luminance of the light emitting element is not reduced, the luminance of the received light emitted from the optical transmission line 5 increases, and in any case, the ratio of the received light by the light receiving element 2 to the emitted light of the light emitting element 1 is further improved. To do.
[0018]
In addition, since the above-mentioned transmission and reception are performed by time division by transmission and reception, the received signal light from the optical transmission path is incident on the light emitting element and affects the oscillation of the light emitting element. There is nothing.
[0019]
According to the present invention, a half mirror or the like is unnecessary and the number of parts is reduced. Moreover, as described above, the reflectance can be adjusted by the multilayer film originally provided on the light emitting surface of the light emitting element, and the reflective film is used to adjust the reflectance on the light receiving surface of the conventional half mirror or light receiving element. There is no need to provide.
[0020]
【The invention's effect】
According to the present invention, the coupling efficiency of the light emitting element, the light receiving element, and the optical transmission path is greatly improved, and the output of the light emitting element can be reduced. Furthermore, the number of parts is small, and it is easy to assemble, and an inexpensive and high-performance bidirectional optical communication module can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of a bidirectional optical communication module of the present invention.
FIG. 2 is an enlarged explanatory view of a light emitting element and a light receiving element part of FIG. 1;
FIG. 3 is an explanatory diagram of an example of a conventional bidirectional optical communication module.
FIG. 4 is an explanatory diagram of another example of a conventional bidirectional optical communication module.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light emitting element 2 Light receiving element 4 Condensing lens 5 Optical transmission line

Claims (3)

Bidirectional optical communication comprising a light emitting element that generates a transmission signal, a condenser lens that couples transmission signal light from the light emitting element to an optical transmission path, and a light receiving element that receives reception signal light from the optical transmission path The light emitting element is provided such that the transmission signal light from the light emitting element is directly coupled to the optical transmission path via the condenser lens, and the received signal light from the optical transmission path is A bidirectional optical communication module, wherein the light receiving element is provided at a position where the light reflected from the light emitting surface of the light emitting element can be received.   The light emitting element is provided on the optical axis of the condenser lens and the light emitting surface thereof is inclined with respect to the optical axis, and the light receiving element has a light receiving surface extending from the optical transmission path. The optical communication module according to claim 1, wherein the module is provided so as to be inclined with respect to a reflected beam of the received signal light by the light emitting element.   3. The optical communication module according to claim 1, wherein a multilayer insulating film is formed on a light emitting surface of the light emitting element, and a reflectance on the light emitting surface is adjusted to 30 to 90% by the multilayer insulating film.

Images